The Rise And Fall Of Combi Mixed Cargo/Passenger Aircraft

The idea of a ‘combi’ aircraft, capable of shifting significant amounts of cargo as well as a good number of passengers, has been around for more than half a century. However, very few remain in service these days, with most of the heavy users already retiring the type. Why did combi aircraft fall out of favor?

KLM combi
Combi aircraft were popular for a time, but now are a rare sight. Photo: KLM

The first combi aircraft

Cargo has always been an essential element of air transportation. From as long ago as the earliest origins of flight, moving mail in a timely manner from city to city was seen as just as important, sometimes more so, than moving passengers. As aviation grew up, cargo remained a critical element of airline economics, with boxes often sharing the same flight as people.

Some of the earliest examples of combined cargo and passenger aircraft were seen with airlines like Northwest Orient. It took delivery of 17 DC-7s between 1957 and 1958, seven of which were the -7CF version which combined ample passenger space with air freight capacity too. The aircraft were modified with a strengthened cargo floor and a forward cargo door being added.

NW Orient DC-7CF
Northwest Orient had some of the first ‘combi’ aircraft in the world. Photo:James Borden Photography Collection via the Northwest Airlines History Center

The trend for ‘combi’ aircraft really evolved from there. In the 1960s and ‘70s, multiple airlines invested in aircraft that could do both jobs adequately well, a trend that was further stimulated by the rise of Boeing as a manufacturer.

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Boeing changed the game

The Boeing 747 was appealing to airlines on several levels. The most significant shift here was its immense size, with a hold capable of swallowing several standard-sized pallets. By 1977, 40 Boeing 747s had been modified to add a cargo door, allowing the aircraft to hold 12 pallets of cargo.

Undoubtedly, the airline that embraced the ‘combi’ philosophy to the greatest extent was Dutch airline KLM. Many of its long-haul routes didn’t have the demand available to fill up a Boeing 747, so filling the wasted space with cargo was a bit of a no-brainer.

KLM Boeing 747-400M
KLM was the biggest user of the 747 combi in the world. Photo: Pieter van Marion via Wikimedia

KLM Invested in seven 747-200 combis, which arrived between 1975 and 1981. These aircraft combined seating for around 200 people with the same cargo volume as a Boeing 707 in full freighter configuration. That was the perfect balance for KLM. The airline upgraded to the 747-300 in the 1980s, adding three to its fleet, and later 15 Boeing 747-400 combis joined the stable.

KLM wasn’t the only airline heavily invested in the idea of combi aircraft. Across the pond, Alaska Airlines was making good use of another Boeing aircraft, albeit a little smaller, to facilitate the important cargo shipments delivered across its milk run flights. Alaska used the 737-400 for this mission, giving it capacity for 72 passengers and four large cargo containers.

Alaska Airlines 737 combi
Alaska Airlines used the 737 combi to deliver essential goods along its milk run routes. Photo: Alaska Airlines

Alaska retired its combis in 2017, and KLM waved goodbye to the last of its 747-400M in the wake of the crisis of 2020. But why did combi aircraft fall out of favor?

The fall of the combi’s popularity

According to an article in Popular Mechanics, the decline of the combi aircraft all started in 1960 when a Yale student wrote a paper. Fred Smith’s paper suggested that there was a fundamental inefficiency in the way air freight was being organized. He said that putting cargo on passenger aircraft and relying on passenger schedules was slowing things down. His suggestion was to create a dedicated fleet working on its own schedule and routes, which could make air cargo an overnight affair.

Reportedly, his professor gave him a C for the paper, considering it to be infeasible. Undeterred, Smith went on to form a company that we know today as FedEx. It took a while for him to size the company up to make a real impact, but he proved his theory right. Dedicated air cargo services became far more attractive, removing the impetus for airlines to operate their own freight services.

The rise of dedicated air freight services has made combis less attractive. Photo: FedEx

The decline of combi aircraft was further impacted by the tragic crash of South African Airways flight 295. The Boeing 747-200B, named Helderberg, was carrying a cargo of mostly electronics from Taipei to Johannesburg along with 124 passengers and crew when a fire broke out in the cargo area. The crew could not control the fire, and it was soon blazing out of control. Many passengers died from smoke inhalation; the rest perished when the aircraft crashed into the sea.

The ensuing investigation from the FAA made it more difficult and expensive to operate combi aircraft. The FAA pushed for these planes to be converted into either all-cargo or all-passenger carriers. When combined with the rise of dedicated cargo airlines, the need and attractiveness of combi planes significantly diminished. While there are still a handful of airlines operating these types of aircraft, the heyday of the combi is well and truly over.